The night before last, I slipped in my friends driveway, fell backwards, and hit my head hard on the concrete (my friend was standing about 6 feet away and she said that she could hear my head hit the driveway). There was no blood, and the pain in my head subsided after about an hour, although I have continued to have mild headaches ever since. My sister who is a nurse checked me out and told me that she doesn't think I have a concussion (I still have normal pupils, speech, brain function, etc). However, yesterday I began experiencing pain in my neck and the base/lower back of my head, and it has become increasingly worse since then. The strange part is, only the left side of my neck hurts. It is somewhat swollen, extremely sensitive to the touch (even in the front by my throat), and I have a very limited range of movement (it hurts to tilt my head back or to the side, etc). My sister thinks that I just have whiplash and that there's not much I can do about it except take ibuprofen, but I can't help but worry that there may be something more serious going on.

Does this sound like something I should seek medical examination/treatment for? Or should I just suck it up and wait for it to get better on its own?